Re: Resonance _s_ Re: Quarter Wavelength Frequency

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Paul Nicholson <paul-at-abelian.demon.co.uk> 

Ed wrote:

 > I question how many of those harmonic resonances would be
 > observed at the input terminals of a long coil with
 > any significant parallel tuning capacitance.

You might be able to count more overtones when the coil is
loaded than when unloaded!  Some that were beyond the range
of the generator will be pulled down into view by the added C.
But others may be harder to see because Q factors and
impedances reduce.

 > Certainly the response will get less and less
 > as the number goes up.

Yes, eventually the overtones peter out as the 'axial' mode
of the coil becomes more and more lossy with rising frequency.
A wave decays away before it can meet its reflection and so
fails to achieve interference and form a standing wave.
Thus the input impedance response stays flat above some cut-off
frequency.  It's like using an open length of some old/lossy
coax as a dummy load for microwaves.

This would be a good point for someone to bring in some
measurements of the spectrum of a primary resonator, say
in the range 0-5Mhz or so.  The secondary would have to be
removed from the scene so that we can be sure we're seeing
primary overtones.  Some readings with and without the primary
capacitor connection would show what's happening to the coil
resonances as terminal reactance is added.  A low-Z generator
in series with the primary ground terminal is required, and
something (scope probe, neon, etc) connected to the hot end of
the coil to pick out the coil activity.

There are already plenty of secondary spectra on various
websites, including tssp - Terry has done lots of those.
So let's focus on the lumpy primary resonator instead.

Hey, an OLTC running with the volts turned down and no
secondary would make a great platform for recording a 'ping'
of the primary into a digital scope.  With its small inductance
and large external C, that very lumpy resonator should make a
tough test of these claims.

I've no doubt that the overtones will be visible.  The issue
is probably one of 'Does any of this matter to the coiler?'

Matt wrote:
 > It should enlighten all, and settle the matter for all but
 > the most die-hard ...

Thanks for your comments.  You know that I don't have any
time or patience for the True Believer and luckily we're not
faced with anything like that.  I see that here and there,
some of the list community's common understanding of coil
resonance is a bit off the mark (although often adequate) in
the technical detail.  Individuals develop a personal
understanding of the physics that they're comfortable with
and which works, apparently.   So it can't be too far wrong
and they're not going to relinquish that just on somebody else's
say-so.  I would expect no one on this list to change their
views without making sure that what is being suggested actually
makes better sense than they already have!  To do that, each
coiler must arrive at a new understanding themselves, not just
take anything on faith.

And of course, any replacement ideas must work as advertised!
I hope that people will go and look for the overtones in
'lumped resonators' and decide the matter on the basis of
what they find.  As often the case, the laws of physics
are not at stake here, it's just a matter of learning how to
apply them correctly to TCs.  Here we're debating which laws
to apply and how.  Experiment can often decide that in cases
where it's not too clear by thought alone.
--
Paul Nicholson
--